This invention relates to switches.
When it is desired to switch an alternating current using a solid-state device, this is conventionally performed by means of triacs. Triacs, however, suffer from the disadvantage that they can be turned on, when they are supposed to be off, by a voltage spike at the supply input. This effect is known as `commutation` and is well-known in triacs to be a disadvantage. Because, once triggered, a triac remains in a conducting state until the supply current ceases, this can lead to the undesired passage of current for a long time, with consequent possible damage to the circuit connected to the output of the triac.
Attempts are usually made to reduce this commutation effect by the use of filters to reduce the triac's exposure to fast voltage spikes or edges. By filtering in this way, however, the amount of useful power that can be passed through the triac is reduced and, because the filter involves bulky inductances and capacitors, the size and weight of the equipment is increased.